Polyurethanes currently prepared in the industry and known in the art generally utilize metal-based catalysts such as stannous and other metal carboxylates. U.S. Pat. No. 5,959,059 to Vedula et al. discloses that suitable polyurethane catalysts include stannous octoate, dibutyltin dilaurate, phenyl mercuric propionate, lead octoate, iron acetylacetonate, and magnesium acetylacetonate. While the melt strength of metal-based catalyzed polyurethane films is sufficient, it would be desirable to further increase melt strength or decrease the melt index.
U.S. Pat. No. 5,908,690 relates to a reportedly breathable and antistatic film produced without a support by extrusion, the film having a DIN friction coefficient of less than 0.8 and consisting of thermoplastic polyurethane elastomer resins with a melt flow rate, as measured at 190° C. under a load of 10 kg, of at most 70, the soft segment of the elastomer resins consisting of polyethylene oxide and/or containing ethylene oxide reaction products and the relative percentage by weight of the soft segment in the polyurethane resin being between 35% by weight and 60% by weight, based on the total weight of the polyurethane used.
WO 97/42248 relates to a rigid thermoplastic polyurethene (RTPU) comprising units of butane diol (BDO) and a polyethylene glycol (PEG) of the type HO—(CH2CH2O)n—H, where n is an integer from 2 to 6. The RTPU of the invention reportedly addresses a problem in the art by providing a potentially lower-cost alternative to an RTPU prepared from hexane diol. The example presented utilizes an organotin catalyst.
U.S. Pat. No. 5,574,092 discloses rigid thermoplastic polyurethanes having a Tg of at least 50° C. having a sufficient concentration of units derived from an aromatic diol to reportedly lower the temperature at which the rigid thermoplastic polyurethane can be melt processed, with a flex modulus of at least 100,000 psi. These rigid polyurethanes are not for use as breathable materials.
U.S. Pat. No. 5,959,059 discloses that tertiary amines such as triethylene diamine can also serve as effective catalysts for polyurethane polymerizations. The amount of the tertiary amine catalyst utilized is very low, and is in the amount from about 50 to about 100 parts by weight per million parts by weight of the end polymer formed. However, the low amount of tertiary amine catalyst has been found to produce less than desirable effects when producing thermoplastic polyurethanes exhibiting reasonably fast kinetics as indicated by suitable low residual amounts of NCO, and low initial melt index values.